Synthetic polymers are broadly used as medical materials. Synthetic polymers are used because they offer easy control of the strengths and structures of materials and easy control of any molding and processing. However, these synthetic polymers have drawbacks in that they often lack affinity for living organisms and lack the inherent bioactivity of biopolymers, for example. To enhance the affinity of the synthetic polymers for living organisms, cells have been caused to adhere to the surfaces of such synthetic polymers, surface treatment has been performed for such synthetic polymers, or such synthetic polymers have been coated or bound with biopolymers (Journal of Biomaterial Science, Polymer Edition. 1993; 4 (3): 217-34, JP Patent Publication (Kokai) No. 61-82760 A (1986); JP Patent Publication (Kokai) No. 4-15063 A (1992); JP Patent Publication (Kohyo) No. 4-503311 A (1992)).
Moreover, JP Patent Publication (Kohyo) No. 11-510399 A (1999) discloses a biomaterial having a thrombus-resistant surface and a method for producing the same. The thrombus-resistant surface is composed of a coating layer of chitosan and 1 or more types of bioactive substance (e. g., polyvinyl alcohol capable of forming a polymer blend with chitosan).
Biopolymers that are polymers existing in living organisms are generally soluble in water. Accordingly, when the surfaces of synthetic polymers are coated with biopolymers, the surface of the synthetic polymer is generally coated with an aqueous solution containing biopolymers by various coating methods such as dip coating or spin coating (Brash, Trans. Am. Soc. Artif. Int. Organs, p. 69, 1974).
When a surface coated with biopolymers with the use of water is embedded within a living organism, biopolymer-derived characteristics are imparted to the surface-coated product at the early implantation stage (e.g., approximately several hours). However, as the time for implantation passes, the problem of the peeling off of biopolymers emerges.
Meanwhile, a technique for binding the functional groups on the surfaces of synthetic polymers to the functional groups of biopolymers using a condensing agent or the like has been studied. According to this technique, the chemical structure is partially altered via application of chemical bonds to biopolymers. Hence, the functions of the biopolymers may be decreased, or any side effect may occur.
Organic fluorine compounds represented by 1,1,1,3,3,3-hexafluoro-2-propanol (HFIP) or trifluoroethanol (TFE) dissolve proteins such as collagen and gelatin. JP Patent Publication (Kohyo) No. 2002-531182 A discloses that a protein matrix for tissue construction is prepared by dissolving the protein and alkyl ester of hyaluronic acid in HFIP and molding the resultant. Also, JP Patent Publication (Kohyo) No. 2004-532802 A and JP Patent Publication (Kokai) No. 2004-321484 A disclose that a structure of protein is prepared by electrospinning. However, only a structure of collagen or gelatin is prepared with the use of this technique, and it is not used for coating of material surface with biopolymers.    Non-patent document 1: Journal of Biomaterial Science, Polymer Edition. 1993; 4 (3): 217-34    Non-patent document 2: Brash, Trans. Am. Soc. Artif. Int. Organs, p. 69, 1974)    Patent document 1: JP Patent Publication (Kokai) No. 61-82760 A (1986)    Patent document 2: JP Patent Publication (Kokai) No. 4-15063 A (1992)    Patent document 3: JP Patent Publication (Kohyo) No. 4-503311 A (1992)    Patent document 4: JP Patent Publication (Kohyo) No. 11-510399 A (1999)    Patent document 5: JP Patent Publication (Kohyo) No. 2004-532802 A    Patent document 6: JP Patent Publication (Kokai) No. 2004-321484 A